While most home labs are small, there are reports of bulk operations in which hundreds of cans of butane can be on-site. Any size lab is a serious danger; first responders should familiarize themselves with the signs of such labs: butane canisters, Pyrex dishes, marijuana, coffee filters, and an extraction vessel that could either be glass or a PVC pipe combination that resembles a pipe bomb.
Hash oil is typically made by packing the castoff leaves and stems of pot plants into a pipe and pouring the highly flammable butane through it. The solvent is then evaporated, leaving a golden color sticky residue that resembles oil or honey. Of course these butane vapors linger in the room where the extraction took place. Only some pretty stupid people would attempt such a process inside an unventilated room.
The resulting mixture of psychotropic plant oil and chemicals is then purified to remove traces of the solvent. One common method of butane removal includes boiling it off in a hot water bath, while another involves the use of a vacuum pump and vacuum chamber to lower butane’s boiling point, pulling butane from the oil.
Although it’s perfectly possible to make hash oil safely, such explosions are the result of a relatively small number of hash oil producers who fail to take even the most basic precautions. The number one precaution is to never make oil indoors.